Accelerators caustic

Xanthates. These compounds (12) are relatively fast accelerators which are used at low temperature because most examples decompose without cross-linking at higher temperature. Xanthates (qv) are produced by reaction of equimolar amounts of alcohol and carbon disulfide in the presence of caustic. The sodium salt is then converted to the 2inc compound or oxidized to the disulfide. 

GB is unstable in the presence of water. Maximum stability in aqueous solutions occurs from pH 4.0—6.5 with the hydrolysis rate increasing as the pH increases. The half-life in distilled water at 25°C is ca 36 h, but hydrolysis is accelerated in the presence of acids or bases. Because bases are far more effective in this respect than acids, caustic solutions are useful for decontamination. 

Diphenyl carbonate, an alternative source of the carbonate group to phosgene, may be obtained by reacting phenol with phosgene in acqueous caustic soda solution, the reaction being accelerated by tertiary amines. The diphenyl carbonate can be purified by redistillation. 

Chemical Reactivity - Reactivity with Water Reacts slowly with water at room temperature to form limewater and oxygen gas Reactivity with Common Materials Heavy metals and dirt can accelerate decomposition to lime and oxygen. The reaction is not explosive Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with water Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Avoid contamination with combustible materials, various inorganic and organic acids, alkalies, alcohols, amines, easily oxidizable materials such as ethers, or materials used as accelerators in polymerizations reactions Stability During Transport Extremely explosion-sensitive to shock, heat and friction. Self-reactive Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent inhibitor of Polymerization Not pertinent. 

Caustic embrittlement corrosion is intergranular, and cracks appear along the grain boundaries. The process is accelerated by ... 

Caustic cracking (caustic embrittlement) Intergranular corrosion affects both carbon steels and austenitic steels and accelerated by high stress, higher temperatures, and impurities in grain boundaries. 

A general term for those types of corrosion induced by caustic and accelerated by stress and moderately high temperatures (200-250 °C). 

The excess of chlorine thus favours formation of HOC1 which in turn accelerates the alternative route to chlorates. The reaction given by Equation 26.3 is significantly faster than that of reaction 26.1, and is strongly exothermic and thus presents runaway potential. This has been avoided historically by providing cooling within the caustic recycle or pump-around loop and by providing an excess of caustic. 

Non-alkaline liquid accelerators are fairly new to the international market, therefore the bibliography on their use is still scarce. They were conceived to solve some classical problems stemming from the use of alkaline accelerators, such as caustic alkalis, hazardous conditions in underground work, risk of alkali-aggregate reaction, risk of handling conventional accelerators with extremely high pH level, and reduction of latter-age strength. 

A coalescer works in the same way as a demister, except that it is used to accelerate the removal of droplets of a heavier liquid from a flowing lighter liquid. An ordinary coalescer is shown in Fig. 26.5. This coalescer was used to remove entrained caustic from a flowing isobutane stream. The liquid isobutane would impact the coalescer pad at a velocity of 1 to 2 ft/min. The droplets of caustic, which have a higher surface tension than isobutane, would adhere to the surface of the coalescer fibers. As the caustic droplets grew bigger and heavier, they would drain down the fibers of the pad, and into the boot. 

Also, the higher the pH, the faster a developer will oxidize. To prevent oxidation, developers often are stored in separate A and B solutions that are mixed just prior to use. Developers using caustic alkali should always be formulated in this manner. Developers containing easily oxidized developing agents, such as pyro, should also be stored this way, regardless of which accelerator is used. 

Uses Accelerator of developing solutions caustic, tending to enlarge grain structure of negatives hypersensitizing films. An emulsion softener causes fog on fast films. 

The use of caustic alkali (e.g., sodium hydroxide) is not recommended with metol as there is a tendency to excessive fog. When used with sulfite alone, without additional alkali (Kodak D-23), metol provides a slow-working, fine-grain developer. This type of film developer often works well with a mild alkali, such as borax, which accelerates the rate of development without increasing the grain size appreciably (Kodak D-25). 

Colloidal palladium eatalytically assists the decomposition of aqueous solutions of hydrogen peroxide, oxygen being evolved. The reaction is monomolecular, and the influence of as minute a quantity of palladium as one gram atom in 26,000,000 litres of solution can be detected with N/60NaOH and N/10H2O2 solution.2 The reaction is accelerated by the presence of caustic soda, the optimum concentration of which is about N/16. In acid solution the peroxide decomposes very slowly. 

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